1. Field of the Invention
The present invention relates to a method for vaporization of liquid organic feedstock and a method for growth of an insulation film, especially to a method for producing a functional organic polymer film that insulates a multilayer wiring gap of a semiconductor integrated circuit. More specifically, it relates to a method for vaporization of liquid organic feedstock made of an organic monomer or an organic oligomer which is a constituent of a functional organic polymer film.
2. Description of the Related Art
A semiconductor integrated circuit is being downsized in designing rule, and consequently deterioration of performance due to delay by wiring is notably observed. That is, a wiring signal delay of a semiconductor integrated circuit is determined with a wiring CR time constant (C: wiring capacity, R: wiring resistance). Because of the increase in wiring resistance due to the decrease in wiring width and the increase in wiring gap capacity due to the decrease in wiring gap, there is a fear that the wiring CR time constant may not come up with the improvement in switching speed of transistors. An aluminum alloy is currently used as a wiring material of a semiconductor integrated circuit. However, owing to the decrease in resistance of a wiring, a copper wiring or a silver wiring has been studied.
Meanwhile, for reducing a wiring gap capacity, an insulation film material having a lower dielectric constant than the existing silica (SiO2) insulation film has been studied. As an insulation film having a low dielectric constant, fluorine-containing silica (SiOF), porous silica and an organic polymer film (organic insulation film) are known. Fluorine-containing silica is problematic in that corrosion of a wiring metal occurs with hydrofluoric acid through a reaction between fluorine in the film and moisture or hydrogen or a dielectric constant is increased by eliminating fluorine. Porous silica is expected because a specific dielectric constant can be less than 2.
However, sometimes, a specific dielectric constant is increased by condensation of moisture to a micro-hole or an insulation pressure resistance is decreased. At present, the development of an organic polymer film excellent in heat resistance and moisture resistance has been in urgent demand as a layer-to-layer insulation film that insulates a multilayer wiring gap on a semiconductor integrated circuit. With respect to the moisture resistance, it is important that a hydrophilic group is absent in an organic monomer, and it is advisable that a polymerization reaction of an organic monomer which is a constituent of the organic polymer film does not undergo a polycondensation reaction of water. The organic monomer herein is a material that, as a structural unit, causes a polymerization reaction to form an organic polymer.
As a method for growth of the functional organic polymer film, there is a spin coating method of an organic monomer (hereinafter referred to as a first ordinary example). This spin coating method has been widely used in growth of an organic polymer film. In this case, an organic monomer is dissolved in a solvent. During film formation, a solvent is removed, and a polymerization reaction proceeds by heating an organic monomer. Consequently, a two-dimensional or three-dimensional network film or a polymer film is formed. An organic monomer dissolved in an organic solvent becomes a structure of an organic insulation film as a product.
For example, a method in which a divinylsiloxanebisbenzocyclobutene polymer film is formed by spin coating is described in, for example, xe2x80x9cREAL-TIME FT-IR STUDIES OF THE REACTION KINETICS FOR THE POLYMERIZATION OF DIVINYLSILOXANEBISBENZOCYCLOBUTENE MONOMERSxe2x80x9d (material Research Symposium Proceeding vol. 227, p, 103, 1991), T. M. Stokich, Jr., W. M. Lee, R. A. Peters (hereinafter referred to as reference 1).
Japanese Patent Laid-Open (JP-A) No. 17006/1999 proposes a method for evaporation of an organic monomer (hereinafter referred to as a second ordinary example) as a method for growth of a functional organic polymer film. In this method, an organic monomer is evaporated, and a monomer in a gaseous phase is polymerized on a substrate to obtain an organic polymer film.
Japanese Patent Laid-Open (JP-A) No. 12532/2000 proposes a method for growth of a polymer film by vaporization of an organic monomer using a carrier gas (hereinafter referred to as a third ordinary example) as a method for growth of a functional organic polymer film. In this method, a polymer film is grown by a step of feeding a liquid organic monomer to a vaporization controller, a step of heating the liquid organic monomer in the vaporization controller, feeding a carrier gas and vaporizing the organic monomer while keeping a partial pressure of the liquid organic monomer lower than a saturated vapor pressure and a step of transporting the carrier gas containing this vaporized organic monomer from the vaporization controller to a reaction chamber, further passing the organic monomer through RF plasma to activate the same and spraying the resulting product on a surface of a substrate mounted in the reaction chamber to grow a polymer film containing the organic monomer in the structure.
Specifically, in the third ordinary example, divinylsiloxanebisbenzocyclobutene (DVS-BCB) is vaporized by feeding 100 to 3,000 sccm of the carrier gas into the vaporization controller held at the total pressure of 20 torr or less, feeding 0.1 to 0.01 g/min of the DVS-BCB monomer into the vaporization controller and heating the mixture at a temperature of 100 to 175xc2x0 C. Further, the vaporized organic monomer is introduced into a plasma gas atmosphere to expedite the polymerization reaction of the organic monomer and decrease the growth temperature of the organic polymer film. The ring opening reaction of the carbon 4-membered ring in the benzocyclobutene structure is started at a lower temperature by generation of plasma to obtain a polymer film made of a three-dimensional polymer chain containing the DVS-BCB monomer in the structure.
The first to third ordinary examples however involve the following problems.
In the first ordinary example, the organic monomer is dissolved in the solvent, and the solution is spin-coated. In the spin coating, approximately 90% of the solution is scattered outside the substrate. Thus, the use efficiency of the feedstock is bad.
Further, the spin-coated film is heated, and the solvent is first removed. Then, the residue is further heated at a high temperature to cause the polymerization reaction of the organic monomer and form the organic polymer film. When oxygen is present in a baking oven, oxygen and a part of the organic monomer are sometimes reacted so that a desired organic polymer film is not formed. For example, a permissible oxygen concentration in spin-coating the solution of the DVS-BCB monomer in mesitylene and then baking the same is 100 ppm or less. For this reason, the whole part of the baking oven has to be purged with a nitrogen gas. Accordingly, this method cannot be realized at low costs.
Still further, dissolved oxygen dissolved in the solvent is sometimes reacted with the organic monomer in the baking. Thus, it is required to strictly control the atmosphere. However, it is difficult to strictly control the atmosphere in the spin coating.
Furthermore, the spin coating is conducted in a spin coating chamber from which a gas is locally exhausted. At this time, floating refuge or fine particles of the organic monomer adhered to the inner wall of the spin coating chamber and dry-solidified are sometimes incorporated into the spin-coated film to degrade the film.
Moreover, the spin coating is problematic in that it requires a large amount of an organic solvent to invite great environmental burden.
The second ordinary example is excellent in that it is quite good in the use efficiency of the raw material in comparison with the spin coating method. However, since the overall liquid organic monomer is vaporized from the gas-liquid interface, it is required to heat a large volume of the organic monomer at a high temperature. Meanwhile, since the organic monomer is reactive, there is a likelihood that the polymerization reaction proceeds at a high temperature and the vaporization of the organic monomer is instable. Thus, it is necessary to improve this instability.
In the third ordinary example, the liquid organic monomer is fed to the vaporization chamber via the monomer feed hole to form a liquid film. Such a liquid organic monomer is heated to a predetermined temperature by a heater, and then contacted with the carrier gas in the vaporization chamber. Incidentally, since the vapor pressure of the organic monomer is increased with the increase in temperature, it is advantageous for the increase in vaporization efficiency. Meanwhile, the organic monomer is increased in its polymerization rate with the increase in temperature. Consequently, when the temperature is too high, the organic monomer is polymerized and solidified before being vaporized.
For the organic monomer to be vaporized satisfactorily without increasing the temperature, the flow rate of the carrier gas is increased. Nevertheless, when the flow rate of the carrier gas fed to the narrow vaporization chamber is increased, there arises a problem that the pressure inside the vaporization chamber is increased owing to the pressure loss of the vaporization chamber.
It is an object of the present invention to provide a method for vaporization of liquid organic feedstock in which liquid organic feedstock can be vaporized in good efficiency.
It is another object of the present invention to provide a method for growth of an organic polymer film made of an organic monomer by activating a vaporization monomer in plasma and polymerizing this monomer on a substrate.
In accordance with the invention, there is provided a method for vaporization of liquid organic feedstock made of an organic monomer or an organic oligomer capable of forming an organic polymer insulation film by feeding the liquid organic feedstock to a vaporization controller, which comprises a first step of mixing the liquid organic feedstock with a carrier gas at a temperature lower than a heat polymerization reaction starting temperature of the liquid organic feedstock to form a gas-liquid mixed fluid, a second step of spraying the gas-liquid mixed fluid on a vaporization vacuum chamber to form an aerosol of the liquid organic feedstock and heating the aerosol, and a third step of vaporizing the liquid organic feedstock through the aerosol.
The aerosol has a diameter of, for example, 100 to 1 xcexcm, and the liquid organic feedstock is, for example, a divinylsiloxanebisbenzocyclobutene monomer. Specifically, in a standard condition, the gas-liquid mixed fluid made of 100 to 500 ml/min of the carrier gas and 0.1 to 0.5 g/min of the liquid organic feedstock is sprayed on the vaporization vacuum chamber held at 1.3 kPa (10 torr) or less, and heated at a temperature of 160 to 250xc2x0 C. to vaporize the liquid organic feedstock.
Further, according to the invention, there is provided a method for growth of an insulation film, wherein a vaporization device for heating an aerosol of liquid organic feedstock to vaporize the liquid organic feedstock through the aerosol and form the vaporized organic feedstock is directly connected with a plasma polymerization reaction chamber, and the vaporized organic feedstock is directly fed to plasma in the plasma polymerization reaction chamber to grow an organic polymer film made of the liquid organic feedstock on a substrate.
In the invention, since the diameter of the aerosol is 100 xcexcm or less, a specific surface area is large, as compared with an ordinary vaporization method in which a liquid film is heated, to increase a vaporization sectional area of the organic monomer, which makes it possible to instantaneously vaporize the same after heating. As a result, the organic monomer can be vaporized at a high temperature and a high vapor pressure to increase a vaporization rate. Moreover, since vaporization can instantaneously be conducted after the heating, the technical problem peculiar to the vaporization of the organic monomer in which the organic monomer is polymerized and solidified by heating at a high temperature can be solved.
Since the carrier gas containing the organic monomer allows the polymerization reaction of the organic monomer on the substrate in the reaction chamber which is closed with a gas exhausted by a pump and to which RF plasma is applied, the organic monomer is not reacted with a reactive gas such as oxygen, nor does deterioration of characteristics such as the increase in dielectric constant owing to oxidation of a part of the resulting polymer film occur.